Dry edible beans are the dried seeds from plants of the Leguminosae family. Beans supply 20% of the worldwide dietary protein. In the United States, approximately 3.5 billion pounds a year of dry edible beans are produced. Beans are low in fat, cholesterol, and sodium and are high in fiber, complex carbohydrates, and proteins. Beans also contain iron, magnesium, calcium, and phosphorus, present in the form of phytic acid.
In processing dry edible beans, the beans must first be rehydrated. Processing the beans gelatinizes the starches, changes the bean texture, improves the availability of proteins and eliminates toxic substances such as lectins, goitrogenic factors, tannins, and trypsin inhibitors. Processing beans also improves their flavor by making them more palatable.
Dry edible beans are low in moisture, typically having between 12% and 14% moisture content. At 50% moisture, a bean becomes easier to process. Bringing a bean from 12% moisture to about 50% moisture is traditionally accomplished by soaking the beans in water. Water enters the bean through the hilum, and seeps around the periphery of the seed coat, causing it to wrinkle. As time continues, the beans hydrate and expand to yield a smooth swollen bean seed. Two to three cups of water per cup of dried bean is often used for soaking. To speed up the soaking process, the temperature of the water can be raised. In addition, an increased soak temperature also aides in a reduction in the cook time by deactivating the enzyme phytase, which would destroy phytic acid that is used in combination with calcium/magnesium to form the soluble salt that is easy to cook. However, increasing the temperature of the soaking water also increases the loss of calcium, magnesium, thiamin, riboflavin, niacin, and some of the oligosaccharides. Over the years, there have been a variety of alternatives proposed to reduce the soak time. They include pressure processes, vacuum infiltration, ultrasonic sound, gamma irradiation, and a combination of sodium chloride, sodium triphosphate, sodium bicarbonate, sodium carbonate and vacuum infiltration. The high sodium content, the degree of tenderization, and the capital investment have all made these methods unattractive.
Another method is a two minute blanch followed by a long soak after removing the heat source. The increase in the initial soak temperature decreases the overall soak time. Unfortunately, many processing companies do not possess a culinary source of hot water or steam. Furthermore, if the soak water is too hard, containing a large amount of divalent ions, the ions will react with the pectin in the bean to form an insoluble salt, which will increase the time necessary to cook the bean since this insoluble layer will work to minimize the amount of absorbed water. Also observed during the processing of beans is discoloration, skin breakage, the development of off-flavors, and the hard-to-cook phenomenon. The addition of ethylenediaminetetracetic acid (EDTA) has been used to improve the color. Sodium bisulfite has also been added to improve the color, however, it also reduces the availability of vitamin B6. Calcium chloride and citric acid have also been added to improve the firmness, color, and brightness of the bean. However, these compounds have resulted in a reduction in the degree of moisture intake due to their creating a firmer outside on the bean. Acids and the addition of salts containing calcium, magnesium, or aluminum toughen the seed coat and reduce the amount of absorbed water. Lastly, sodium carbonate (NaHCO.sub.3) has been added to improve the degree of tenderization by breaking down the hemicellulose, yet it also destroys the B vitamins present.
The food industry has often used enzymes in a variety of situations. Specifically, carbo-hydrase and cellulase enzymes are used in preparations of starch syrups and dextrose, alcohol, beer, ale, fruit juices, chocolate syrups, bakery products, liquid coffee, wine, dairy products, cereals, and spice and flavor extracts. The carbo-hydrase and cellulase enzymes can safely be used in foods.
One carbo-hydrase and cellulase enzyme that is commercially available is Viscozyme.RTM. L, a multienzyme complex containing a wide range of carbohydrases. Viscozyme.RTM. L can be used to break down cell walls so that useful components can be extracted from plant tissues. This enzyme functions at low temperatures which results in a reduced energy demand and less thermal degradation of the desired materials. Viscozyme.RTM. L is particularly useful for processing plant materials in the alcohol, brewing, starch, and related industries. The enzyme has the ability to liberate bound materials and degrade non-starch polysaccharides which improves starch availability in fermentation and reduces viscosity, thus improving yields. The optimum conditions for the activities of this enzyme are a pH of between 3.5 and 5.5, and a temperature of about 40.degree. to 50.degree. C.